1. Field of the Invention
The present invention relates to fluid power control valves and more particularly, but not by way of limitation, to a hydraulic multiple flow selection valve.
2. History of the Prior Art
Fluid power engineers are constantly confronted with the need for being able to drive fluid motors, and particularly hydraulic motors at different speeds.
The typical motor is a positive displacement motor or also known as a constant displacement motor that can be varied only by increasing the fluid flow rate through the motor. This can be accomplished by either increasing the fluid pressure causing the higher flow rate and in turn requiring larger volume present at the motor or by being able to connect several pumps in parallel to increase the flow rate through the motor.
The first solution, that of varying the pressure is often impractical since the fluid sources available are also used to operate ancillary equipment such as hydraulic jacks, rams or the like which must operate on a lower or at least substantially constant pressure.
The second solution of varying the volume flow rate is usually accomplished through a plurality of parallel and series connected valves putting one or more hydraulic pumps on the line in connection with the motor. This solution is costly and increases and likelihood of system failure due to the introduction of many separate components.
Another problem associated with the use of several valves is that of hydraulic shock encountered by not being able to "feather" or gradually bring in a new volume rate by simultaneously opening and closing several valves.
There are infinitely variable speed control systems commercially available but again are often impractical due to their being expensive and difficult to maintain.